In order for a mobile station (MS) to operate in a High Rate Packet Data (HRPD) or a CDMA 2000 3G1X communication system, the MS must first obtain configuration information and access parameters information associated with the system, typically by capturing one or more overhead messages, such as an Access Parameters Message (APM) and/or a Sector Parameters Message (SPM), that is broadcast over a forward link control channel. The overhead message further includes a sequence number corresponding to a version of the information included in the message. Whenever the network changes any of the configuration information or access parameters information in the overhead message, the network indicates the change by updating the associated sequence number in all messages that carry the associated sequence number.
When an MS activates in a HRPD or a CDMA 2000 3G1X system, or roams into an associated network, the MS captures the overhead messages and obtains the current configuration information, access parameters information, and sequence numbers from the overhead messages. The MS then stores the captured configuration information, access parameters information, and sequence numbers in a memory of the MS. When the MS subsequently determines to attempt to access the network, that is, to originate a call or to respond to a page, the MS conveys an access probe to the network. However, sometimes, prior to conveying the access probe, the MS must first confirm that the configuration information and access parameters information maintained by the MS are up-to-date. In order to confirm the currency of the maintained information, the MS tunes to a forward link control channel and checks a sequence number of an overhead message. If the sequence number does not match the value maintained by the MS, then the MS realizes that it must update one or more of the configuration information and/or access parameters information stored by the MS and listens for one or more new overhead messages with the updated sequence number(s). Upon receiving the new overhead message(s), the MS updates the stored configuration information and/or access parameters information. The MS may then proceed to convey the access probe to the network via an access channel.
In addition, there may be overhead messages that do not include a sequence number corresponding to a version of the information included in the message, such as a ANSI-41 RAND Message (RANDM) in CDMA 2000 3G1X. When the system requires that the MS be authenticated prior to providing the MS access to a network of the system, the RANDM includes a global token that is a part of the access parameters information used by the MS to authenticate itself. In this case, the MS must always receive the RANDM before it may proceed to convey the access probe to the network via an access channel, regardless of the sequence number values for configuration information and access parameters information.
Current standards provide for an MS to perform a persistence test before actually transmitting on the access channel during an access channel cycle. The persistence test is based on a persistence value (PSIST) broadcast via an overhead channel and stored by each MS tuned to the overhead channel. In performing the persistence test, the MS generates a random number and compares the random number to the broadcast persistence value. If the random number is less than the persistence value, then the persistence test is deemed to be successful and the MS attempts to transmit on the access channel during a corresponding access channel cycle. If the random number is equal to or greater than the persistence value, then the persistence test is deemed to be unsuccessful and the MS holds off transmitting and repeats the persistence test during a next access channel cycle.
A particular overhead message may be transmitted by a network as infrequently as every 1.28 seconds and the supervision time interval for all system parameters messages may be as long as 5.12 seconds. When the network updates any of the network's configuration information and/or access parameters information, the update is reflected in an updated sequence number and all MSs seeking to originate a message or respond to a page will obtain such updated information via one or more subsequent overhead messages and then attempt to access the network via the access channel. The longer the period between an overhead message, the greater the number of MSs that are likely to determine to originate a connection or respond to a page in a time period substantially immediately after the last required overhead message. The persistence value, and correspondingly the persistence test, is insensitive to a number of MSs simultaneously attempting to access the access channel. As a result, the greater the number of MSs that simultaneously seek to access the network after capturing a same overhead message and updating their configuration information and/or access parameters information, the greater the likelihood of collisions as multiple MSs successfully perform a persistence test and attempt to access the access channel during a same access channel cycle. With a possible wait for an overhead message of 1.28 seconds after determining to originate a message or to respond to a page, or an average wait of 0.6 seconds, followed by a transmission of an access probe, a collision of the access probe with other access probes and a determination that the access probe was unsuccessful, and a retransmission of the access probe, the delay in call set up can become significant.
Therefore, a need exists for a method and apparatus that reduces a likelihood of access probe collisions when multiple MSs attempt to access a network after updating configuration information and/or access parameters information via a same overhead message.